0062-B3

Selection of hydrological indicators for sustainable management of forest plantations based on catchment monitoring

Carla Daniela Câmara ¹, Maria do Carmo Calijuri ¹, Walter de Paula Lima ² and Maria José Brito Zakia ²

Abstract

Results of hydrological monitoring carried out from January 1999 to July 2001 in two catchments are evaluated in terms of water quality and streamflow hydrograph analysis. The objective is to select hydrological variables of water quality that can function as potential indicators of sustainable forest management. The study is based on comparative analysis of data obtained monthly in two experimental catchments located in Imperatriz, in the Brazilian state of Maranhão (05^o 23'S). One of the catchments has an area of 239 ha and is covered with native forest; the other has an area of 95 ha and is covered with eucalyptus plantation. The selected stream water quality variables were nitrate, phosphorus, suspended sediments and turbidity. These were significantly higher in the stream of the eucalyptus plantation catchment. Confidence intervals for the monitored variables results were established for allowing future comparisons, such as after changes in the forest cover in one of the catchments. The intervals estimated had the following values:

The intervals will permit to infer whether land use changes will be responsible for changes in streamflow and water quality, as related to the results obtained in the native forest catchment, or even related with the previous conditions in the same catchment. Based on hydrograph analysis, peakflows were similar in both catchments.

Introduction

Fast growing tree plantations have been the center of widespread discussions about their possible environmental effects, mainly in relation to water consumption and water quality deterioration.

In this regards, a suitable method for the measurement of these hydrological aspects is through the use of experimental catchments (Likens et al., 1977; Swank & Johnson, 1994). Within the contemporary paradigm of sustainable forest management, the process of monitoring should be oriented to the identification and validation of environmental indicators, measured at the catchment level, which could signal the conditions and tendency of the environment as caused by forest management activities (Walker et al., 1996). Sustainable management, in this sense, will involve forest production plus the maintenance of catchment health, collectively measured by hydrological processes, soil productive capacity and riparian ecosystem resilience (Lima & Zakia, 1998; Gunderson, 2000). The objective is essentially to devise management practices that minimize environmental impacts and protect soil, water and catchment values.

In Brazil some investigations have been conducted in experimental catchments, mainly with the objective of monitoring hidrological effects of management practices of fast growing forest plantations, in terms of water quantity and water quality parameters (Oliveira, 1989; Scardua, 1994; Azevedo, 1995; Vital, 1996; Zakia, 1998; Câmara, 1999; Oki, 2002). These studies are being conducted in different soil and climatic conditions and collectively provide interesting information about water quality impacts resulted from forestry activities. Among the many physical and chemical water quality parameters being monitored, some of them are very sensitive to management practices, which constitutes a very good characteristic for them to function as environmental indicators (Prabhu et al., 1998).

The question of indicators of sustainable forest management is not so simple, though, since we are dealing with complex systems. Suitable indicators, for instance, have to include different levels of organization of the biological systems (Bollmann et al., 2000), as well as the different scales of sustainability. On the other hand, a good indicator will also have to present other important characteristics, such as: cost effectiveness, relevance to the assessment or monitoring objectives, efficiency in delivering meaningful information about the ecological systems (Walker & Reuter, 1996; Prabhu et al., 1998).

The use of experimental catchment as a methodological approach for the monitoring of hydrological indicators is also very adequate for dealing with the question of scales of sustainability, as illustrated in Table 1 (Lima & Zakia, 1998). As given in Table 1, we can assess the effects of forest management practices, occuring at the forest management unit level, through the monitoring of hydrological variables measured at the streamflow. But these same variables can also be influenced by processes at other scales in the catchment, such as the destruction of the riparian ecosystem. Therefore, it is important to develop indicators at each of these levels (Prabhu et al., 1998)

Table 1: Different scales of hydrological indicators for sustainable forest

Site specificity has also to be considered when dealing with catchment environmental monitoring, for any proved indicator on a given region may present a different range of variation in other conditions (Walker & Reuter, 1996).

Finally, a most intriguing point in the use of hydrological indicators for sustainable forest management is related to the very definition of sustainable management. This can be quite difficult, but all definitions involve value judgements based on the prevailing amount of knowledge about ecosystem functioning. In another words, we will never be able to prove that a given forest management practice is sustainable, but only whether it is leading towards sustainability or not. Therefore, a most essential characteristic of the use of indicators of sustainable forest management is in the context of adaptive management system. Sustainable forest management is, thus, a state of permanent learning from the outcome, or the information provided by monitoring. In this sense, using experimental catchments for the monitoring of hydrological indicators for sustainable management of forest plantations can be done in comparison with similar results obtained with the simultaneous monitoring of a control, undisturbed catchment, in order to separate the effects of management activities.

Using such approach, the present study has the objective of comparing the results of hydrological monitoring of two catchments in the region of Imperatriz, State of Maranhão, Brazil, in order to identify water quality and peakflow variables potentially suited as indicators of catchment health. One of the catchments is covered with the secondary tropical forest and the other was planted with Eucalyptus. The hypothesis is that the native forest catchment presents better conditions for the maintenance of catchment values, in terms of water quality and streamflow regime.

Material and Methods

The experimental catchments are located in the municipality of Imperatriz, State of Maranhão, in Brazil (05^o 23'S). Average annual temperature is around 26.4 ^oC, with minimum of 21.1 ^oC and maximum of 32.4 ^oC. Average annual precipitation is 1.453 mm (Sentelhas, 2002). The main soil type is Red -Yellow Podzol

One of the catchment, with an area of 80.9 hectares, is covered with five-year old Eucalyptus plantation. As required by the Brazilian Forest Code, the riparian vegetation was maintained undisturbed. The control catchment has 239.91 hectares and is almost entirely covered with native tropical forest (85%), having 15% of its area also planted with Eucalyptus.

Stream-gaging station is composed of a tranquilizing pond, a 45 cm type H flume, an automated streamflow recorder and a semi-automated water sampler. Water samples are colected weekly and water quality analysis follows standard methods (Franson, 1995) and include the following parameters: phosphate, nitrate, calcium, magnesium, potassium, turbidity, conductivity and suspended sediments.

Data Analysis

The data analyzed encompass the period from february 1999 to june 2001. First, we considered the hydrologic functioning of the native forest catchment as adequate for the maintenance of stable streamflow regime and good water quality. Then, we selected the best variables for the monitoring as those which differed significantly between the two catchments. This selection was made through the non-parametric Mann-Whitney test (Ayres et al., 2000).

In the sequel, we then established confidence intervals for the physical and chemical water quality parameters for the data from the two catchments, using the Wilcoxon test, which is also a non-parametric test for the comparison of paired data sets obtained in different ocasions (Campos, 1976; Ayres et al., 2000).

The confidence intervals were established for allowing future comparisons, such as after changes in the forest cover in one of the catchments. The intervals will permit to infer whether such changes will cause changes in streamflow and water quality, as related to the results obtained in the native forest catchment, or even related with the previous conditions in the same catchment.

For the similar comparison between of the stormflow response between the catchments, we selected three rainfall events and the corresponding streamflow hydrographs, which were graphically compared.

Results and Discussion

Table 2 shows the estimated confidence intervals for the physical and chemical water quality parameters between the two catchments. The results between the two catchments were significantly different for nitrate, phosphorus, calcium, potassium, magnesium, suspended sediments and turbidity. The values of turbidity, suspended sediments, phosphorus and nitrate were higher in the Eucalyptus catchment. On the other hand, the concentrations of calcium, potassium and magnesium were higher in the native forest catchment. Conductivity did not differ between the catchments.

Table 2 - Confidence intervals for physical and chemical streamflow water quality parameters in the catchments with native forest and eucalyptus plantations in Imperatriz, State of Maranhão, Brazil.

The native forest cover appears to produce better hydrological protection, in terms of water quality, as related to the lower values of nitrate, phosphorus and sediment losses. The fast growing eucalyptus, on the other hand, may explain the lower concentration of calcium, potassium and magnesium in the streamflow of this catchment.

In a study in an agricultural catchment protected with a riparian buffer zone, Lowrance et al. (1984) observed a stable nutrient balance in terms of the input by precipitation, the internal transport via overland flow, and the losses through streamflow. They concluded that the buffer zone filtering efficiency was in the following decreasing order: nitrate, calcium, clhorine, magnesium, phosphorus and potassium, explaining that the riparian ecosystem had very good conditions for the denitrification process. In a similar study, Peterjohn & Correl (1984) observed that nitrogen losses occur mainly through subsurface runoff, whereas phosphorus and sediments losses are mainly driven by surface runoff. In the present study, it can be seen in Table 2 that the maintenance of riparian buffer zone in the eucalyptus plantation catchment, as required by law, was not in itself sufficient to maintain the stream water concentrations of suspended sediments, phosphorus and nitrate in the same level as in the native forest catchment. These results reinforce the consensual conclusion that the search for sustainable management of forest plantation must involve a systemic approach, including conservational practices and appropriate indicators in different scales, one of which is the maintenance of the riparian ecosystem buffer zone (Lima et al., 1999; Simões, 2001).

Figures 1 and 2 show the stormflow hydrographs of two rainfall events, comparatively between the two catchments. The native forest catchment has an area almost 2.5 times greater than the eucalyptus catchment and this difference explains the observed differences in discharges rates. However, the figures show that the pattern of stormflow responses between the two catchments is very similar, which indicates that the reforestation with eucalyptus was not responsible for any significant modification of the surface permeability of the catchment, in terms of this integrated evaluation of the processes of infiltration and percolation.

Figure 1 - Streamflow responses of the catchments with native forest and eucalyptus plantation during a storm of 142 mm in march 29, 2000.

Figure 2 - Sreamflow responses in the catchments with native forest and eucalyptus plantation during storms of 73 mm in January 09, 2000, and 42, mm in January 25, 2000.

Conclusions

Among the studied water quality parameters, turbidity, suspended sediments, nitrate and phosphorus can be selected as better indicators for the monitoring of sustainable forest management.

The comparative analysis of peak-flows and stormflow responses of the catchments can be considered a systemic indicator of the integrated effects of forest management practices in the catchment. In the present study, the hydrologic conditions of the catchment planted with eucalyptus was not significantly modified, as based on this hydrograph analysis.

The maintenance of the integrity of the riparian ecosystem in this tropical environment appears to be a required conservation practice. However, the efficiency of such conservation strategy, which reffers to the catchment scale (meso scale), depends on the simultaneous use of sustainable land use and forest management practices at the scale of the forest unit management (micro scale).

Aknowledgements

Thanks are due to the following: a) Celmar S/A Industria de Celulose do Maranhão, for the cooperative partnership in this project; b) FAPESP - Fundação de Amparo a Pesquisa do Estado de São Paulo (State of São Paulo Research Foundation), Process N^o 00-00746-2; c) CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico (National Research Council), Process N^o 550270/2002-7, CTHIDRO.

References

Azevedo, E. C. 1995. Vazão e características físicas e químicas do deflúvio de microbacias hidrográficas cobertas com mata nativa pastagem e Eucalyptus grandis.. Dissertação (Mestrado). Universidade Federal de Viçosa. Viçosa, 92 p.

Ayres, M., Ayres, M. J., Ayres, D. L., Santos, A. S. 2000. Bio Estat 2.0 Aplicações nas áreas de ciências biológicas e médicas. Belém: Sociedade Civil Mamirauá; Brasília: CNPq, 272 p.

Bollman, H. A. 2000. Bases para a estruturação de indicadores de qualidade de águas. Revista brasileira de recursos hídricos, 5 (1): 37 - 60.

Câmara, C. D. 1999. Efeitos do corte raso de eucalipto sobre o balanço hídrico e a ciclagem de nutrientes em uma microbacia experimental. Dissertação (mestrado). Escola Superior de Agricultura "Luiz de Qeiroz" - Universidade de São Paulo. Piracicaba, 87 p

Campos, H. 1976. Estatística experimental não paramétrica. 2.ed., Piracicaba: ESALQ,. 344p.

Franson, M. A. H. 1995. Standard Methods for the Examination of Water and Wastewater. Washington: American Public Health Association, 1268 p.

Gunderson, L.H. 2000.Ecological resilience - in theory and application. Annual review of ecology and systematics, vol. 31: 425-439,

Likens, G. E.; Borman, F. H., Pierce, R. S., et al. 1977. Biogeochemistry of a forested ecosystem. NewYork: Springer-Verlag,. 146 p.

Lima, W. P. & Zákia, M. J. B. 1998. Indicadores hidrológicos em áreas florestais. Série Técnica IPEF, 12, n. 31, p. 53 - 64, abr.

Lima, W.P.; Zakia, M.J.B.; Camara, C.D.; Ferraz, F.F.B; Giusti, C.C. 1999. Indicators of soil and water conservation for sustainable forest management in the neotropics. In: Conferencia y taller internacional sobre indicadores de manejo forestal sostenible en el neotropics. Turrialba: IUFRO/CATIE. P. 1-16..

Lowrance, R.; Todd, R.; Fail JR., J.; Hendrickson JR., O.; Leonard, R. & Asmussen, L., 1984. "Riparian Forests as Nutrient Filters in Agricultural Watersheds". BioScience, 34 (6): 374-377.

Oki, V. K. 2002. Impactos da colheita de Pinus Taeda sobre o balanço hídrico, a qualidade da água e a ciclagem de nutrientes em microbacias.,. Dissertação (mestrado). Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo. Piracicaba, 71 p.

Oliveira, F. A. 1989. Produção e qualidade da água em microbacias contendo diferentes coberturas vegetais na região de Agudos. Dissertação (mestrado). Escola Superior de Agricultura Luiz de Queiroz - Universidade de São Paulo. Piracicaba, 96 p.

Peterjohn, W. T. & Correl, D. L., 1984. "Nutrient Dynamics in an Agricultural Watershed: Observations on the Role of a Riparian Forest". Ecology, Durham, 65 (5): 1466 -1475.

Prabhu, R.; Ruitenbeek, H,J,; Boyle, T.J.B.; Colfer, C.J.P. 1998. Between voodoo science and adaptive management: the role and research needs of indicators of sustainable forest management. In: International conference on indicators for sustainable forest management. Melbourne: IUFRO/CIFOR. P. 1-17.

Scardua, F. P. 1994. Caracterização hidrológica de uma microbacia hidrográfica experimental da Estação Experimental de Ciências Florestais de Itatinga, ESALQ/USP. Dissertação (Mestrado). Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo. Piracicaba, 93 p.

Sentelhas, P. C., Pereira, A R., Marin, F. R., Angelocci, L. R., Alfonsi, R. R., Caramori, P. H., e SWART, S. Balanços hídricos de 500 localidades brasileiras. Núcleo de monitoramento agroclimático, Depto. De Ciências Exatas, ESALQ/USP: home page: http://ci.esalq.usp.br

Simões, L. B., 2001. "Integração entre um modelo de simulação hidrológica e sistema de informação geográfica na delimitação de zonas tampão ripárias". Tese de Doutorado. UNESP/Botucatu. 171p.

Swank, W. T., Vose, J. M., Elliot, K. J. 2001. Long-term hydrologic and water quality responses following commercial clearcutting of mixed hardwoods on a southern Appalachian catchment. Forest Ecology and Management, n. 143, p. 163 - 178.

Vital, A. R. T. 1996. Efeito do corte raso no balanço hídrico e na ciclagem de nutrientes em uma microbacia reflorestada com eucalipto.. Dissertação (mestrado) Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo. Piracicaba,. 106 p

Walker, et. al. 1997. Catchment health indicators: na overview In: WALKER J. & REUTER, D. J. Indicators of catchment health: a technical perspective. CSIRO: Australia, p. 4 - 18.

¹ Departamento de Hidráulica e Saneamento, Escola de Engenharia de São Carlos University, of São Paulo, Cxp. 359 CEP13566-590 São Carlos, S.P. Brazil. [email protected]

² Departamento de Ciências Florestais, Escola Superior de Agricultura "Luiz de Queiroz", University of São Paulo Cxp. CEP530 13400-970 Piracicaba, S.P. Brazil.